Study of Tecovirimat for Human Mpox Virus

This phase 3, randomized, placebo-controlled, double-blind clinical trial evaluated the efficacy of tecovirimat for the treatment of mpox. Participants who had or were at higher risk for severe disease because of their age or medical history, were pregnant or breastfeeding, or were taking medications that could have decreased their exposure to tecovirimat were assigned to receive open-label tecovirimat for 14 days. All other participants were randomized 2:1 to receive either tecovirimat or placebo for 14 days.

Randomized participants who reported severe pain 5 days after randomization (on Day 6) or later or progressed to severe disease stopped blinded study treatment and started a 14-day course of open-label tecovirimat.

Participants self-monitored lesions daily through 28 days (Day 29) or resolution, whichever came first, and completed a daily pain scale and symptom diary. Study visits occurred weekly through 28 days (Day 29) and included safety and skin assessments and specimen collections. A final study visit occurred at 56 days (Day 57) to assess for recrudescence of infection (development of new lesions after initial resolution of disease).

Version 3 of the protocol gave participants the option to enroll and complete study visits remotely. Participants did not provide specimens at remote visits.

On November 26, 2024, the Data and Safety Monitoring Board (DSMB) recommended that the study close due to statistical futility. The study team and sponsor agreed with the DSMB's recommendation and the study closed to accrual on November 27, 2024. The primary analysis report forming the basis of the primary manuscript used data from follow-up visits occurring through October 23, 2024, the data cutoff for the November 2024 DSMB review (the primary completion date). Outcome measures submitted to clinicaltrials.gov were also based on data from follow-up visits occurring through October 23, 2024, and summaries of participant flow, baseline characteristics, and adverse events submitted to clinicaltrials.gov were based on data from follow-up visits occurring through February 22, 2025 (the study completion date).